Security and safety at national and international transportation facilities such as airports, train-stations and waterports has become of vital importance. Ensuring the safety and integrity of transported items such as baggage, packages, shipments, etc. continues to be a major challenge for transportation and commercial commerce industries. X-ray irradiation methods have been developed for screening transported items for the presence of illicit and/or harmful materials, however, such methods are often slow and laborsome and further give no indication as to whether an item has been inspected, nor confirms that screening has been completed. Simple confirmation methods are desired which indicate the safety and integrity of transported items.
Prior art describes a color-indicating X-radiation dosimeter based on the color change of dyes by radiation-induced chemical reactions. These indicators are used typically for radiation sterilization of food and other items. Such sterilization procedures require very large X-ray doses, several orders of magnitude greater than X-irradiation levels used in transportation security systems.
The prior art also describes radiochromic films such as GafChromic HD-810, a thin almost colorless radiochromic diacteylene monomer, coated on a transparent polyester base that undergoes solid-state polymerization when irradiated with X-rays. The radiation-induced polymerization of the colorless film leads to the formation of a deep blue product. An FWT-60 series of radiochromic dosimeters are designed such that thin colorless films containing aminotriphenyl methane dyes gradually change to deep blue in relation to absorbed X-ray dose. However a limitation of the HD-810 and FWT-60 films is that they are also photochromically responsive to ultraviolet light and ambient light. Exposure of these films to indoor or outdoor lighting conditions, before or after X-ray exposure, will result in a color change. Therefore it would not be possible to determine if the color change was due to an inspection by an airport X-ray scanner or ambient light.
U.S. Pat. No. 4,489,240 describes a radiochromic leuco dye dosimeter that includes a plastic tube containing a solution of a radiochromic dye, which is sensitive to ionizing radiation. A change in optical density of the solution is employed to measure the radiation-induced adsorption of the leuco dye. This last step requires a spectrophotometer and would be expensive and cumbersome to employ in the transportation industry.
Soviet Union Patent 277123 describes a chemical ionizing radiation dosimeter that uses a composition containing tri-phenyl tetrazolium chloride. US patent application 2001/00462-75 A1 describes a nonrotating X-ray system and methods for three-dimensional, three parameter imaging of objects for the purposes of identifying non-intrusively their material content. The system and methods are useful, for instance in detecting explosives, narcotics, or other contraband materials in passenger luggage or shipped parcels.
While providing color-indicating X-ray dosimetry, the prior examples do not describe a method to verify that transported items were indeed X-rayed. This is particularly critical when airport luggage is held for any period of time between X-raying and loading onto the plane. Therefore it is desirable to develop tamperproof X-radiation indicators to provide positive visual verification that an item has been subject to X-radiation. This is particularly useful in airports and other transportation centers. It is also desirable that such indicators are easily attached to the screened item such as aircraft, train, bus, or cruise ship luggage and packages and be tamperproof, and provide immediate, recognizable changes upon X-radiation. The advantage of such a system is convenient visual verification of the radiation treatment, prevention of fraud, and proof of proper examination. A further requirement of such an indicator is the ability to be sensitive to X-radiation, and show no photochromic effects due to other forms of electromagnetic radiation (also referred to as radiation or light) including ultraviolet, visible, infrared, microwave, radiowave, and ambient light. An additional requirement is an indicator that will immediately show evidence of a color change and will require no additional chemical or physical processing steps to observe the color change after X-ray exposure. Such a verification system is also handy to distinguish between exposed and unexposed X-ray cassettes in medical and other X-ray imaging.